The reason I bring this up is that I a grant I manage had a researcher from this unit - Dr. David Gray who himself is confined to wheelchair - and while the subject was not pain he might be able to (or his colleagues) might be able steer you in the right direction.
The Children's Hospital in DE is another great resource and they may still see a 19 year old. It's the Alfred I DuPont Hospital for Children http://www.nemours.org/internet?pid=3&cat=1. They see all sorts of conditions in children including those unfortunate to have lost a limb to disease or accident. They have a good PT program as well (or did over 20 years ago when I had to rehab an nasty knee). Give them a call.
Other suggestions - major research hospitals - I forget the name of one in either Houston or Dallas, or Johns Hopkins - then there's the Mayo Clinic (also in Fl) - however I think that this deserves research before running out there!
Lastly, Walter Reed is doing a lot of work - or more realistically has a lot to do with - amputees. It may be worth while placing a call. Having volunteered there, I can say that the staff there (or at least the ones I interacted with in the Family Assistance Center) are caring and compassionate.
Best - Alix